Handle code_cache dir creation in libnativebridge

Also:

- add kPreInitiliazed state to native bridge with check transition:
kOpened->kPreInitialized->kInitialized
- made sure we free the memory for the code_cache_path
- tidy up some error messages
- tidy up tests
- add a dummy native bridge to test with

Bug: 18027433
Bug: 18097480

Change-Id: I39f74c93580f2e224080dd3df2ffaa9cf9f8cd9c